explicitly report errors in MainThreadFlipperReceiver

Summary: Use responder rather than allowing exception to propagate.

Reviewed By: jknoxville

Differential Revision: D14538883

fbshipit-source-id: 2774a2adfcee356e1853fa3bf3c01aa113181262

android/src/main/java/com/facebook/flipper/plugins/common/MainThreadFlipperReceiver.java

@@ -9,32 +9,47 @@ package com.facebook.flipper.plugins.common;
 
 import android.os.Handler;
 import android.os.Looper;
-import com.facebook.flipper.core.ErrorReportingRunnable;
 import com.facebook.flipper.core.FlipperConnection;
 import com.facebook.flipper.core.FlipperObject;
 import com.facebook.flipper.core.FlipperReceiver;
 import com.facebook.flipper.core.FlipperResponder;
+import java.io.PrintWriter;
+import java.io.StringWriter;
 
 public abstract class MainThreadFlipperReceiver implements FlipperReceiver {
 
   public MainThreadFlipperReceiver(FlipperConnection connection) {
-    this.mConnection = connection;
+    // TODO(T41065412): remove unused constructor argument.
   }
 
-  private final FlipperConnection mConnection;
   private final Handler mHandler = new Handler(Looper.getMainLooper());
 
   @Override
   public final void onReceive(final FlipperObject params, final FlipperResponder responder) {
     mHandler.post(
-        new ErrorReportingRunnable(mConnection) {
+        new Runnable() {
           @Override
-          public void runOrThrow() throws Exception {
+          public void run() {
+            try {
               onReceiveOnMainThread(params, responder);
+            } catch (Exception ex) {
+              responder.error(
+                  new FlipperObject.Builder()
+                      .put("name", ex.getClass().getCanonicalName())
+                      .put("message", ex.getMessage())
+                      .put("stacktrace", getStackTraceString(ex))
+                      .build());
+            }
           }
         });
   }
 
+  private static String getStackTraceString(Throwable th) {
+    StringWriter stringWriter = new StringWriter();
+    th.printStackTrace(new PrintWriter(stringWriter));
+    return stringWriter.toString();
+  }
+
   public abstract void onReceiveOnMainThread(FlipperObject params, FlipperResponder responder)
       throws Exception;
 }

android/src/test/java/com/facebook/flipper/plugins/common/MainThreadFlipperReceiverTest.java

@@ -0,0 +1,51 @@
+/*
+ *  Copyright (c) 2018-present, Facebook, Inc.
+ *
+ *  This source code is licensed under the MIT license found in the LICENSE
+ *  file in the root directory of this source tree.
+ *
+ */
+package com.facebook.flipper.plugins.common;
+
+import com.facebook.flipper.core.FlipperObject;
+import com.facebook.flipper.core.FlipperResponder;
+import com.facebook.flipper.testing.FlipperConnectionMock;
+import com.facebook.flipper.testing.FlipperResponderMock;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+
+@RunWith(RobolectricTestRunner.class)
+public class MainThreadFlipperReceiverTest {
+
+  FlipperConnectionMock connection;
+  FlipperResponderMock responder;
+
+  @Before
+  public void setup() throws Exception {
+    connection = new FlipperConnectionMock();
+    responder = new FlipperResponderMock();
+  }
+
+  @Test
+  public void errorIsPassedToResponder() throws Exception {
+    MainThreadFlipperReceiver receiver =
+        new MainThreadFlipperReceiver(connection) {
+          public void onReceiveOnMainThread(FlipperObject params, FlipperResponder responder)
+              throws Exception {
+            throw new RuntimeException("hello exception");
+          }
+        };
+
+    receiver.onReceive(new FlipperObject.Builder().build(), responder);
+
+    Assert.assertEquals(1, responder.errors.size());
+    FlipperObject error = responder.errors.get(0);
+    Assert.assertEquals("hello exception", error.getString("message"));
+    Assert.assertEquals("java.lang.RuntimeException", error.getString("name"));
+    Assert.assertTrue(
+        error.getString("stacktrace").contains(MainThreadFlipperReceiver.class.getCanonicalName()));
+  }
+}